Enhanced UV Penetration and Cross‐Linking of Isoporous Block Copolymer and Commercial Ultrafiltration Membranes using Isorefractive Solvent

Amphiphilic block copolymers are promising candidates for the fabrication of ultrafiltration membranes with an isoporous integral asymmetric structure. The membranes are typically fabricated by the combination of block copolymer self‐assembly and the non‐solvent‐induced phase separation (SNIPS) process resulting in isoporous integral asymmetric membranes. Certainly, all these membranes lack thermal and chemical stability limiting the usage of such materials. Within this study, the fabrication of completely cross‐linked isoporous integral asymmetric block copolymer membranes is demonstrated by UV cross‐linking resulting in chemical and thermal stable ultrafiltration membranes. The UV cross‐linking process of PVBCB‐b‐P4VP (poly(4‐vinylbenzocyclobutene)‐b‐poly(4vinylpyridine)) block copolymer membranes in dependency of irradiation time, intensity, distance between membrane and UV source and the wavelength is investigated. Furthermore, it is shown that the penetration depths can be increased by soaking the membranes in wave‐guiding solutions before UV cross‐linking is carried out. Moreover, a completely new and easy cross‐linking strategy is developed based on isorefractive solvents resulting in thermal and chemically stable membranes that are cross‐linked through the whole membrane thickness. Finally, the new cross‐linking strategy in isorefractive solutions is transferred to commercial PVDF and PAN‐co‐PVC polymer membranes paving the way for more stable and sustainable ultrafiltration membranes. A membrane in an isorefractive solution is becoming transparent and being penetrated by UV light. The membrane becomes invisible when its refractive index matches that of the solution so that the UV light is able to pass through the membrane due to its transparency. The membrane is crosslinked to the hole extent of the polymeric part while in the dry state, the UV light is reflected so that the crosslinking occurs only to a few nanometers depth.